Dumbell



FIG. 1 is a top plan view of a dumbbell showing my new design, the side opposite being identical;

FIG. 2 is a side elevational view thereof, the other three sides are identical;

FIG. 3 is a top plan view, identical to FIG. 1; and

FIG. 4 is a perspective view of the dumbbell.

The broken line showing of a human hand in FIG. 3 is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a dumbbell, as shown and described. 